Field of the Invention
The present invention relates to a start-up control device and a start-up control method for a power plant having a steam turbine.
Description of Related Art
Starting time of a steam turbine power plant is required to be further reduced for stabilizing the system power connecting to renewable energy represented by wind power generation or solar power generation and for cutting fuel costs and reducing environmental load.
As the temperature and the flow rate of steam are rapidly increased at the time of starting the steam turbine, the surface of a turbine rotor is increased in temperature as compared with the inside thereof and a temperature gradient in a radial direction is increased, as a result, thermal stress is increased. If low-cycle thermal fatigue accumulated in the turbine rotor due to the thermal stress exceeds a limit value of a material of the turbine rotor, a crack can occur in the turbine rotor. The low-cycle thermal fatigue accumulated in the turbine rotor during each start-stop cycle can be defined by a decrement of a turbine rotor lifetime due to thermal stress, that is, a lifetime consumption rate (LC). Here, the lifetime consumption rate will be 100% when the crack can occur in the turbine rotor due to the low-cycle thermal fatigue.
There is a fixed correlation between a peak value (σmax) of thermal stress generated in one start-up and the lifetime consumption rate (LC) of the turbine rotor by the start-up. When a stop time of the steam turbine becomes long, the temperature inside the turbine rotor is reduced by natural cooling. As a result, the thermal stress at the time of start-up is increased, and the lifetime consumption rate is increased accordingly. Therefore, it is necessary to suppress the increase of thermal stress by increasing the starting time for suppressing the increase of the lifetime consumption rate.
When the power plant starts operation, the annual number of start-up times and a standard lifetime consumption rate per one start-up (a planned value of the lifetime consumption rate) in a current year are determined such that an integrated value of the lifetime consumption rate does not exceed 100% within the number of operation years of the power plant, and a thermal stress limiting value is set based on the planned value of the lifetime consumption rate.
The start-up control of the power plant is executed based on a predetermined start-up schedule. The start-up schedule includes start-up control parameters such as boiler ignition, steam turbine start-up, turbine speed-up, heat soak, load increase, start time of load retention and a turbine rotational speed increase rate, a generator output increase rate, heat soak time and load retention time from the beginning of start-up until reaching a target load, which are set such that the peak value of thermal stress during start-up does not exceed the thermal stress limiting value.
As related-art techniques relating to the control method of power plant, there are techniques described in JP-A-2009-30476 (Patent Document 1) and JP-A-2-181001 (Patent Document 2).
According to a method and a system for optimizing operation of a power plant disclosed in Patent Document 1, in a multipurpose optimization problem of calculating an operation amount at the time of operating the power plant so as to satisfy constraint conditions of both or one of the operation limiting values of respective apparatuses of the power plant and an environmental regulation value of the plant in consideration of target functions as plural evaluation indexes, repeated calculation due to experience or trial and error by a decision maker who is an engineer or an operator can be reduced as well as the optimum operation amount which can satisfy the decision maker can be calculated in a short period of time.
Furthermore, according to a starting operation support system for a thermal power plant disclosed in Patent Document 2, it is possible to create a start-up schedule capable of accurately keeping a start-up completion time (combining time or target load reaching time) and suppressing thermal stress which is the most important operation constraint condition at the time of starting the turbine within a prescribed value to thereby shorten a necessary time for starting (abbreviated to as a starting time) to the minimum. Even when schedule slips due to unexpected factors such as occurrence of abnormality, a schedule as close to the original schedule as possible can be created after the factor is solved based on the prediction of thermal stress of the turbine, therefore, the slippage of start-up completion time can be suppressed as small as possible.